Cold-working lubrication



United States Patent f 3,296,844 COLD-WORKING LUBRICATION Frank B. Quinlan, Richland, Wash, assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Filed Feb. 18, 1963, Ser. No. 259,467 7 Claims. (CI. 7242) The invention described herein was made in the course of, or under, a contract with the United States Atomic Energy Commission.

The invention relates to a novel method of surfacetreating metals for drawing and other cold-working operations, more particularly to such a method employing a novel combination of lubricants whereby cold-working is facilitated in an economical manner.

In carrying out drawing, reaming, tube-forming and other cold-working operations on metals, no lubricant has been discovered that will give satisfactory results under all conditions. Since cold-working causes metals to gain in yield strength, increasingly greater pressure is required at each successive pass to bring about the reduction of cross sectional area, or other desired deformation. Hence a lubricant that gives good results during the early passes may fail later, and permit the metal being cold-worked to be scored, or to cause damage to the die, mandrel, reamer, or other cold-working device. This can happen regardless of the metal being cold-worked; even ferrous and copper alloys are not entirely exempt from these difiiculties and, as might be expected, they are more troublesome in the case of less ductile metals such as molybdenum and nickel and of softer metals such as aluminum.

In the case of the so-called exotic metals, which have come into use during recent years, the difliculties arising from the failures of conventional lubricants are of such an aggravated character as to amount to a prohibition against relying on them alone. Included in this class of metals are zirconium, uranium, titanium, tantalum and their alloys. The only previously known method by which these metals can be cold-worked is by giving them a chemical treatment whereby their surface is transformed into a compound such as a fluoride or phosphate, which, with the aid of conventional lubricants, is capable of withstanding the cold-working. This is expensive and is undesirable when highly purified metals are required.

It is, accordingly, the general object of the invention to provide a method of cold-working metals.

It is a more particular object to provide a lubricant for cold-working metals.

It is a still more partcular object to provide a method of cold-working metals of the class consisting of zirconium, zirconium alloys, uranium, uranium alloys, titanium, titanium, titanium alloys, tantalum and tantalum alloys, without chemically altering the surfaces thereof.

According to the invention, metals are prepared for cold-working by first coating the surface with a thin undercoat of asphalt, over which is placed a top coating of a dry lubricant such as one selected from the class consisting of lithium stearate, calcium stearate, sodium stearate, molybdenum disulfide, colloidal graphite and tale. The surfaces thus prepared are then subjected to cold-working directly, without the need to recoat them between successive passes through the die or other cold-working device, one surface preparation normally sufficing for the entire process. After the cold-working has been carried out, the material remaining on the workpiece may be simply removed with a hydrocarbon, chlorinated hydrocarbon or other such organic solvent, since no chemical changes are involved.

In carrying out the invention the asphalt used should have a high melting temperature, such as between 225 and 300 F. It may be applied in any known manner such as brushing, dipping, spraying or the like. I prefer 3,296,844 Patented Jan. 10, 1967 to apply it by dissolving the asphalt in a solvent since this makes for an undercoat of uniform thickness. The thickness of the undercoat depends on the type of cold-working being done; in drawing wire, for example, the finer the wire, the thinner should be the unndercoat. In drawing very fine wire, a solution of 35 grams of asphalt per liter of xylene produces an undercoat which performs well. When drawing rods half an inch or greater in diameter, asphalt in xylene should have a paint-like consistency. Other suitable solvents in addition to xylene are benzene, toluene, mineral spirits, trichloroethylene, perchloroethylene, carbon tetrachloride and the like.

When an asphalt solution is used to coat the metal, the solvent should, of course, be evaporated before proceeding further. This can be hastened by applying heat in an oven, but heating is not necessary.

When applying the second coating of a dry lubricant, such as from the class above enumerated, an important consideration is to avoid contaminating the asphalt coating. Minute specks of grit, or minute drops of oil or grease are enough to destroy the protective properties of the asphalt. It is therefore necessary to apply the dry lubricant with care such as by placing some on a clean cotton cloth and rubbing this into the surface of the asphalt. A few quick strokes of the dry lubricant-bearing cloth sulfice as long as the entire area is covered. No harm, however, will result if an excess amount is applied, since it will either fall oif as dust, or be scraped off in the die, or other coldworking device. The only material appearing to have any beneficial effect is the first minute layer that adheres to the surface of the asphalt.

Coolant water may, or may not, be used in connection with my invention. In some cases it is unnecessary, but in others, where an unusually large amount of heat is generated, it is advisable.

I have found by trials that when lithium stearate is applied over asphalt this permits an over 300% increase in drawing speed as compared to when only [asphalt is used. The other dry lubricants above listed produce similar effects, though less pronounced. They all have special advantages; sodium stearate and calcium stearate are cheaper than the others, and hence may be used when economy is a prime consideration. Molybdenum disulfide, while not permitting as great drawing speed as the others, is capable of withstanding greater pressures; hence it may be used in later passes after the metal has become strengthened by the cold-working, although, of course, the working speed must then be reduced. Colloidal graphite and talc may also be used at this stage, and in some cases may withstand even greater pressures than molybdenum sulfide.

To avoid the slowdown just described, the wire, or other shape, may be annealed after yield strength has built up to an undesirable value; the yield strength will subside thereby, making it possible to work faster, using lithium stearate, or one of the other stearate dry lubricants. However, this expedient may be undesirable in some cases, since annealing may cause contamination of highly purified metals.

As can be seen, there appears to be some kind of a synergistic effect between the asphalt and the dry lubricants. Together they give results in excess of the sum of what they can do separately. Theoretical explanations of this have been offered, but since none of these have been demonstrated conclusively, it would serve no useful purpose to set them forth at the present time; and my invention is therefore offered empirically, on the basis of actual experiments.

Example I Part of a lot of highly work-hardened Zircaloy-Z rods, inch in diameter, were coated with a xylene solution of paint-like consistency of asphalt having a melting temperature of about 225 to 300 F. Zircaloy-2 is an alloy consisting of about 1.5 weight percent (w/o) Sn, about 0.12 w/o Fe, about 0.10 w/o Cr, about 0.05 w/o Ni, and the balance Zr. The xylene was evaporated to leave a hard coating of asphalt and no further coating was added.

The rods were passed through a die with a spray of coolant water at the die to produce a cross-sectional area reduction. No drawing speed in excess of 10 feet per minute was possible.

Example II The remainder of the lot of rods mentioned in Example I were treated in the same way as those in Example I except that a coating of lithium stearate was applied with a clean cotton cloth after the xylene was evaporated. The drawing apparatus operated easily at its maximum drawing speed of feet per minute.

Example III A sintered rod of ultra pure molybdenum, /2 inch in diameter and approximately three feet long, was to be drawn down to the smallest possible diameter. An intermediate anneal was not permitted because of the risk of contamination.

The rod was coated with a xylene solution of paint-like consistency of asphalt having a melting temperature of about 225 to 300 F. This was permitted to stand at room temperature until the asphalt hardened, and then lithium stearate was applied with a clean cotton cloth. The rod was then drawn through a series of dies of successively decreasing diameter with a water spray, no further asphalt nor lithium stearate being reapplied between passes. After the cross-sectional area of the rod had been reduced by drawing was commenced through a die making a further 5% reduction; in this operation chattering began. Without removing the rod from the die, molybdenum disulfide wlas rubbed into the remaining portion of the rod with a cotton cloth. Upon resumption of the drawing no chattering was observed and the drawing proceeded smoothly.

Example IV A uranium wire ,4 inch in diameter was to be drawn to 10 mils. It was coated with a solution of 35 grams of asphalt having a melting temperature of about 225 to 300 F., per liter of xylene, and dried with heat. The asphalt-coated wire was then coated with molybdenum disulfide in a clean cotton cloth and passed through a series of dies of decreasing diameter. No renewal of either the asphalt or the molybdenum disulfide coatings was made. After a few passes friction resulted in excessively slow drawing speed. On the next pass colloidal graphite was applied to the wire, which reduced friction slightly, but as the 10 mil diameter was approached the wire broke at one point. The wire was then cleaned, given a high alpha anneal, undercoated with asphalt in the same way as before, and then coated with lithium stearate in the same way. Reductions then proceeded smoothly.

Example V coating a second coating consisting essentially of dry lubricant.

2. The method of claim 1 wherein the dry lubricant is selected from the class consisting of lithium stearate, sodium stearate, calcium stearate, molybdenum disulfide, colloidal graphite and talc.

3. A method of drawing fine wire selected from the class consisting of zirconium, zirconium alloys, uranium, uranium alloys, titanium, titanium alloys, tantalum and tantalum alloys, comprising applying to the wire a first coating consisting essentially of a solution having a first solvent selected from the class consisting of aromatic hydrocarbons and chlorinated aliphatic hydrocarbons with asphalt melting between 225 and 300 F. dissolved therein, evaporating the first solvent, applying to the first coating a second coating consisting essentially of dry lubricant, drawing the wire through successively smaller diameter dies, and removing the first and second coatings with a second solvent.

4. The method of claim 3 wherein the first solvent is selected from the class consisting of xylene, toluene, benzene, trichloroethylene, perchloroethylene, and carbon tetrachloride.

5. The method of claim 4 wherein the dry lubricant is selected from the class consisting of lithium stearate, sodium stearate, calcium stearate, molybdenum disulfide, colloidal graphite, and talc, and the second solvent is selected from the class consisting of hydrocarbons and chlorinated hydrocarbons.

6. A method of drawing fine wire selected from the class consisting of zirconium, zirconium alloys, uranium, uranium alloys, titanium, titanium alloys, tantalum and tantalum lalloys, comprising applying to the wire a first coating consisting essentially of a solution having a solvent selected from the class consisting of xylene, toluene, benzene, trichloroethylene, perchloroethylene, and carbon tetrachloride and about 35 grams of asphalt having a melting point between about 225 F. and about 300 F. per liter of solvent, evaporating the solvent, applying to the first coating a second coating consisting essentially of lithium stearate, drawing the wire through dies of successively smaller diameter until chattering begins, applying to the second coating a third coating consistng essenally of molybdenum disulfide, dnawing the wire through dies of successively smaller diameter, and removing the first, second and third coatings with a solvent selected from the class consisting of hydrocarbons and chlorinated hydrocarbons.

7. A metal shape selected from the class consisting of zirconium, zirconium alloys, uranium, uranium alloys, titanium, titanium alloys, tantalum and tantalum alloys, having a first coating consisting essentially of asphalt melting between 225 and300 F. and a second coating consisting of dry lubricant.

References Cited by the Examiner UNITED STATES PATENTS ALFRED L. LEAVITI, Primary Examiner. RALPH S- K xam ner, 

3. A METHOD OF DRAWING FINE WIRE SELECTED FROM THE CLASS CONSISTING OF ZIRCONIUM, ZIRCONIUM ALLOYS, URANIUM, URANIUM ALLOYS, TITANIUM, TITANIUM ALLOYS, TANTALUM AND TANTALUM ALLOYS, COMPRISING APPLYING TO THE WIRE A FIRST COATING CONSISTING ESSENTIALLY OF A SOLUTION HAVING A FIRST SOLVENT SELECTED FROM THE CLASS CONSISTING OF AROMATIC HYDROCARBONS AND CHLORINATED ALIPHATIC HYDROCARBONS WITH ASPHALT MELTING BETWEEN 225* AND 300*F. DISSOLVED THEREIN, EVAPORATING THE FIRST SOLVENT, APPLYING TO THE FIRST COATING A SECOND COATING CONSISTING ESSENTIALLY OF DRY LUBRICANT, DRAWING THE WIRE THROUGH SUCCESSIVELY SMALLER DIAMETER DIES, AND REMOVING THE FIRST AND SECOND COATINGS WITH A SECOND SOLVENT.
 7. A METAL SHAPE SELECTED FROM THE CLASS CONSISTING OF ZIRCONIUM, ZIRCONIUM ALLOYS, URANIUM, URANIUM ALLOYS, TITANIUM, TITANIUM ALLOYS, TANTALUM AND TANTALUM ALLOYS, HAVING A FIRST COATING CONSISTING ESSENTIALLY OF ASPHALT MELTING BETWEEN 225* AND 300*F. AND A SECOND COATING CONSISTING OF DRY LUBRICANT. 